What are some good acid catalysts to use for the addition of amines to ketones and aldehydes? (organic chemistry)

Addition of amines to ketones requires an acid catalyst to protonate the carbonyl oxygen in order to polarise the carbonyl group for reaction to take place at a reasonable rate. However the amines can also be protonated to form ammonium salts, which can then not perform nucleophilic attack on the carbonyl. It turns out that actually the fastest rate of reaction occurs when the pH is such that half of the amine is protonated, and the ammonium salt acts as the acid catalyst. In order to control this, a strong acid is preferred as full dissociation offers greater control of the pH over weaker acids. Therefore an acid such as HCl is often used. Alternatively, H2SO4 (sulfuric acid) can be used as it is a strong acid, and as it is a dehydrating agent can also shift equilibrium further toward the product as water is formed in this reaction, so by Le Chatelier's principle removing it shifts equilibrium to the products.

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